1. Field of the Invention
This invention generally relates to methods and apparatus for testing optical systems and particularly to devices and techniques for the automated measurement of radii of curvature of a variety of optical surfaces including those of optical elements themselves as well as those used to form them.
2. Background of the Prior Art
Throughout the process for fabricating optical systems from simple to more complex, it is frequently necessary to determine if, and how well, a variety of optical surfaces conform to their designers stated expectations. Not only does the performance of optical systems in final form need to be verified but various parameters of their components need to undergo intermediate testing for conformance prior to their final assembly in the system. Indeed, even the tools of fabrication, especially molds for the formation of plastic or glass lens elements, need to be tested for compliance with design specifications.
One of the most frequently encountered measurements that needs to be made is that of the radius of curvature of a spherical surface in either convex or concave form. Classically, this measurement is made through the use of a hand-held instrument called a spherometer which measures the sagittal height (sag) of the surface over a known diameter and then displays the radius of curvature on a dial or other visual display after an internal calculation which relates radius to sag height and the known diameter. However, the accuracy of such devices are prone to relatively large errors because sag heights are usually small dimensions that are difficult to accurately measure mechanically.
A more accurate technique for radii measurement involves the use of an auto-collimating microscope in an arrangement referred to as a radiusscope. Here, one first focuses on the surface to be measured and then on the center of curvature of the surface where a reticle image has been formed back on itself by reflection from the test surface. The positions of the microscope are recorded, and the difference between them represents the radius of curvature to limits of accuracy which depend on the preciseness of the length measurements and the ability of the operator to accurately focus on the reference points.
Where the spherometer suffers from problems of precision, the use of the radiusscope, which can be accurate to microns if care is taken, is time consuming and dependent on operator skill and experience.
Consequently, there is a need for an instrument for the rapid and accurate measurement of radii of curvature, and it is a primary object of the present invention to provide such a device.
Another object of the present invention is to provide methods and associated devices for automatically measuring radii of curvature and other parameters of optical surfaces with minimal dependence on operator skill.
Yet another object of the present invention is to provide an automated instrument for providing statistical analysis of quality in high volume production settings.
Still another object of the present invention is to satisfy all of the foregoing objects with a user friendly device that is simple in its implementation and low in cost.
Other objects of the invention will in part be obvious and will in part appear hereinafter. A full understanding of the invention will best be had from reading the detailed description to follow in connection with the detailed drawings.